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No. 753,508. 1 PATENTBD MAR-1, 1904. T. Z. MILLARD & P. H. ALMER. LIGHTMEASURING INSTRUMENT.

AHFLIGATION FILED MAB-. 23. 19034 HO MODEL.

24 5 in e 55 :25

UNITED ST TES Patented March 1, 1904.

PATENT: OFFICE. Y-

THOMAS Z. MILLARD, OF OTTUMWA, AND PHIL HAROLD PALMER, OF BLOOMFIELD,IOWA; SAID MILLARD ASSIGNOR TO SAID PALMER.

LIGHT-MEASURING INSTRUMENT.

SPEGIFICATLON forming part of Letters Patent No. 758,508, dated March 1,1904.

Application and March 23,1903.

- photometer that will directly indicate the in-- tensity of lighttransmitted to it and also to directly indicate the relation of theintensity of light emitted from an electric lamp to the current consumedby said lamp. vVlre attain this by applying a retarding force orretarding forces to the rotation of the vane in an ordinary radiometerin such a manner that the vane instead of revolving completely aroundits axis will move through an angle the greatness of which depends uponthe intensity of light striking the vane. Thus thefintensity of saidlight is directly indicated upon ascale calibrated along said angle.

The accompanying drawing shows a vertical section of the instrument bywhich we attain the foregoing objects I v The instrument consists of anair-tight bulb G, around which is fastened a coil of insulated wire P P,and on the inside of the bulb G is a very light vane consisting of anabsol-bent of light.D and a reflector of light C, attached one to eachend of a magnetic needle A, which is attached perpendicularly to aspindle B, which rests in sockets wt and n. The air is exhausted fromthe bulb to a degree at which the vane will most readily move under theforce of light. Also included with the instrument is the adjustablesupport consisting of a base R, on which there is an adjustable clamp S,which clamps to a semicirculai' rod T, which supports the bulb G andcoil P P. i

The end E of the magnetic needle A is made heavier than the other end,so that the vane Serial No. 149,218. (Ht model.)

will seek acertain position of equilibrium when the instrument issupported inan in-.

clined position and the vane is acted upon by ment by means of clamp S.so that the spindle B is vertical, the force of gravity will not retardthe rotation of the vane, and the force of magnetism from the current inthe coil will act alone as a retarding force against the force of lighton the vane. Then by passing the current of an electric lamp whose lightshines against the vane of the instrument through the coil the relationof the intensity of light emitted by the lamp to its current consumptionwill be indicated by the position of the vane. Scales may be calibratedupon the bulb at V and V. x

Between the source of light to be measured and the instrument-isinterposed an alum-cell -which hinders the obscure heat-rays whichmay'radiate from the source of light from reaching the instrument. Asheat has. a tendency to rotate the vane, temperature corrections maybemade by the adjustment of inclination of instrument by means of clamps.

We are aware that the intensity of light has been measured by the speedof rotation of the vanes in radiometers; but to the best ofour knowledgewe are the first to apply the prin- I ciple of repulsionand attractionoflight on reflectors and absorbents of light in such 21- 5 manner thatthe intensity of light will be indicated directly with success, makinga. direct reading photometer and efficiency-indicator.

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to secure by Letters Patent, is

The combination in a radiometer of a vane of 5 be What we claim as ourinvention, and desire In testimony whereof we have signed our names tothis specification in the presence of IO two subscribing witnesses.

THOMAS Z.-MILLARD.

PHIL HAROLD PALMER:

which amagnetic needle made with one end avier than the other is a part,a coil of insulated Wire the plane of which coincides with Witnesses:the axis of the vane and an ad ustable sup- W. S. CHESINAN, port, allsubstantially as shown.

B. W. SCOTT. v

